Known mechanisms have been proposed for providing properties of hysteresis to a clutch disc for transmitting torque from an engine to a transmission on the basis of an elastic deformation of coil springs.
For example, JPH07-054291A describes a construction in which properties of hysteresis are generated by supporting and sandwiching a drive ring 40, which is engaged with a spring 90 within a closed ring 36, between friction rings 38, 39 at one side of a hub 13.
JPH09-112569A describes a hysteresis mechanism which securely causes sliding friction with a fiction plate 122 , a mechanism in which projecting portions of a first friction member 120 and a second friction member 121 are engaged at both ends of a flange 105, and the first friction member 120 and the second friction member 121 are rotated unitarily with the flange 105.
JPH10-103407A describes a construction in which properties of hysteresis are generated in two steps by dividing a bush at one side into a first bush 16 and a second bush 18 and by causing friction between, on the one hand, the first bush 16 and a hub 2 and, on the other hand, the second bush and a separate flange 5.
Hysteresis mechanisms of clutch discs described in JPH09-112569A and JPH10-103407A are constructed on the presumption that opposing surfaces of a thrust member (e.g., a friction member, or a bush) and a friction surface of a hub (e.g., a friction plate, or a separate flange) make contact uniformly at plane surfaces, generate frictional force, and generate properties of hysteresis.
The thrust member is most often formed by injection molding with resin in order to reduce manufacturing costs and weight, and an opposing surface of the thrust member may also in these circumstances be formed by injection molding. In these circumstances, the opposing surface is not necessarily formed uniformly, either because of cooling contracture during injection molding, which becomes the cause of dispersion during manufacturing, or because of uneven dents caused by the configuration of the thrust member. Surface waviness and warping may thus on occasions be generated at the opposing surface.
In other words, when the thrust member having surface waviness and warping on the opposing surface is applied to a hysteresis mechanism of a clutch disc described in JPH07-54921, JPH09-112569, or JPH10-103407, the opposing surface of the thrust member does not make contact uniformly with the frictional surface of the hub (e.g., the friction plate or separate flange). Properties of hysteresis are accordingly dispersed when the clutch disc is initially assembled and thus there has been a danger of the properties of hysteresis not being able to perform an adequate level of torsion cushioning performance of the clutch disc.